Persistent conductivity and positive charging characteristics of a zinc oxide photoconductor

ABSTRACT

Electrophotographic recording material containing photoconductive zinc oxide treated with urazole or one of its derivatives and processes of electrophotographic recording using such materials. These materials are characterized by low-memory effect, improved charging characteristics and are capable of accepting either positive or negative charges to obtain either positive or negative copies.

United States Patent lnventors Robert Joseph Noe Mortsel; Jozef Frans Willems, Wilrijk; Albert Lucien Poot, Kontich; Karel Eugeen Verhille, Mortsel, all of Belgium Appl. No. 831,253 Filed June 6, 1969 Patented Jan. 11, 1972 Assignee Gevaert-Agfa N.V.

Mortsel, Belgium Priority June 6, 1968 Great Britain 27,045/68 PERSISTENT CONDUCTIVITY AND POSITIVE CHARGING CHARACTERISTICS OF A ZINC [50] Field ofSearch 96/].7, 1.8, 106, l, 1.5; 252/501; 260/2404 [56] References Cited UNITED STATES PATENTS 3,245,786 4/1966 Cassiers et al. 96/] 3,455,684 7/1969 Depoorter et al. 96/1 .7 3,507,692 4/1970 Ghys et al. 1 17/201 FORElGN PATENTS 836,148 6/1960 Great Britain 96/l.8

Primary Examiner-George F. Lesmes Assistant Examiner-M. B. Wittenberg Attorney-William J. Daniel ABSTRACT: Electrophotographic recording material containing photoconductive zinc oxide treated with urazole or one of its derivatives and processes of electrophotographic recording using such materials. These materials are characterized by low-memory effect, improved charging characteristics and are capable of accepting either positive or negative charges to obtain either positive or negative copies.

PERSISTENT CONDUCTIVITY AND POSITIVE CHARGING CHARACTERISTICS OF A ZINC OXIDE PHOTOCONDUCTOR This invention relates to light-sensitive recording materials comprising as light-sensitive substance a photoconductor.

Photoconductive binder-type coatings prepared by incorporating a finely divided photoconductor in a binder are well known.

Commonly used are electrophotographic materials containing a photoconductive layer comprising photoconductive zinc oxide dispersed in an insulating binder. Said layer is coated on a sufficiently conductive support, e.g., a clay-coated or glassine-type paper base from a paintlike coating mixture by conventional paper coating techniques. Since the zinc oxide has a brilliant white color it forms an excellent base for contrasting with the developer materials applied to it. Moreover zinc oxide is relatively less expensive and can be spectrally sensitized by a great variety of dyes. However, as already explained in the United Kingdom Pat. No. 1,020,504 filed Dec. 29, 1961 by Gevaert Photo-Producten N.V., zinc oxide possesses the less interesting property of having a relatively low dark-resistivity. Hence, in order that the electrical conductivity of a photoconductive recording layer based on photoconductive zinc oxide shall be sufficiently small in the dark for retaining an electrostatic charge during the time needed for exposure and development, it is usual to incorporate in the recording layer some other substance with a higher electrical dark-resistivity.

For that purpose and by the need of a photoconductive recording layer with sufficiently mechanical strength a binding agent is used improving the dark-resistivity of the recording layer.

According to said United Kingdom Patent, zinc oxide is treated with certain organic phosphorous compounds, preferably organic oxyacids of phosphorus improving the dark-resistivity of the photoconductive zinc oxide grains. By that treatment it is possible to use a large number of binding agents and even such type of binding agents that have no very low electrical conductivity. As a further result of that treatment the photoconductive recording layer is less sensitive to variations in relative humidity and may contain a much higher amount of photoconductive zinc oxide so that an optimum sensitivity is reached.

Unfortunately the introduction of said organic phosphorous compounds gives rise to a rather large memory effect," i.e., to a rather large residual conductivity in the time after exposure.

Quantitatively speaking the memory effect is expressed here by the ratio of the periods of time (1 and t respectively) elapsing before by electrostatic corona charging in the absence of light 90 percent of the maximal charge level is attained on a photoconductive recording layer that has not been exposed previously (time 1,), respectively 90 percent of the maximal charge level is attained on the same photoconductive recording layer (time t that immediately before its charging had received an exposure to active light sufiicient to remove a charge that has been applied in a previous step.

The present invention is based on the discovery that the treatment of photoconductive zinc oxide with a compound (treating agent) corresponding to the following general formula (including its salt and tautomeric structures):

wherein:

each of R, and R represents hydrogen, an alkyl group including a substituted alkyl group, an aryl group including a substituted aryl group, an acyl group including a substituted acyl group, e.g., an aliphatic acyl group (alcoyl) or substituted aliphatic acyl group, e.g., an acetyl group, or an aromatic acyl group (aroyl), e.g., a benzoyl group, including a substituted aromatic acyl group, or a heterocyclic nucleus including a substituted heterocyclic nucleus, e.g., a pyridine nucleus, or a thiazole nucleus, or R and R together represent the necessary atoms to close a fused ring or ring system,

Z the atoms necessary to close a fiveor sixmembered heterocyclic ring including such ring in substituted form and including such ring making part of an either or not substituted fused ring system, and

X represents oxygen or imino, and at least one of the nitrogen atoms making part of the ring closed by Z carries a hydrogen atom, that optionally may be replaced by a cation when using the compound in salt form, increases the dark-resistivity of a recording layer containing such zinc oxide and gives rise to a small memory effect. The said treatment improves the chargeability of a photoconductive recording layer containing photoconductive zinc oxide with a negative corona and moreover besides the possibility of negative corona-charging offers the unexpected possibility of positively corona-charging the recording layer and obtaining thereon positive electrostatic charge images.

In preferably used compounds according to said general formula Z represents a group, wherein R represents hydrogen or a hydrocarbon radical, e.g., an alkyl radical including a substituted alkyl radical or an aryl radical including a substituted aryl radical, and X represents oxygen or imino.

Most preferred compounds according to said general formula are urazole and urazole derivatives wherein at least one nitrogen atom in the ring carries a hydrogen atom.

Thanks to the property of the recording material according to the present invention of being capable to be charged positively as well as negatively, it is possible with one and the same developer, e.g., an electrophoretic developer with toner particles possessing a particular sign of charge, to reproduce one and the same original at will as a positive or negative copy depending on the sign of the electrostatic charge applied to the recording layer of said recording material.

Thus, it is possible e.g., starting from a microfilm original to prepare positive as well as negative enlarged copies.

The same effects as described above were obtained when the photoconductive zinc oxide is mixed with other photoconductive substances, e.g., the photoconductive chalkogenides of cadmium more particularly photoconductive cadmium sulphide, crystalline mixed cadmium sulphide selenide and cadmium selenide. The said chalkogenides may be doped, e.g., with zinc in order to increase their photosensitivity.

A small memory effect of the recording material is advantageous in cases in which the recording material before its image-wise exposure accidentally or not is overall-exposed to daylight or in which the recording material has to be used in a multicolor reproduction system, wherein the recording layer is several times successively charged and exposed, e.g., through halftone selection transparencies of the multicolor original to be reproduced.

According to a practical method of determining the memory-effect the recording material is to be tested is fixed onto a rotating disk whereon it is successively carried under a corona charging unit and under a probe or electrode, wherein a charge is induced being directly proportional to the one present on the recording layer (ref. Cassiers, J. Phot. Sci., 10 1962) 58).

The time (t,) of reaching percent of the maximal charge level is noted and then the recording material after maximal charging is exposed till complete discharging. Practically immediately thereafter charging is repeated and again the time is noted for reaching 90 percent of the second maximal level which normally is not as high as the one obtained in the first charging step. A usual rotating speed of the disk is 750 or complexated form or its tautomeric configuration. since also in these forms an interaction with the photoconductive zinc oxide probably forming a zinc salt can take place.

In order to achieve an optimum effect, the treating agent is r.p.m.

Treating agents which have proved to be particularly useful 5 preferably contacted in dissolved form with the photoconducare listed hereafter. g 93 jS E;

TABLE Z- N-Rz Melting No. of point, compound R R: Z X C l H H C ONH O 244 2 II H ('3NH N H 206 H 3 I}? H C ONH- 300 4 H H CON 0 206 5 H H C ON- 0 170 I1- 4H9 6 H G CONH O 263 7 CH: Same Same O 183 s H H CON- 0 193 1H5 9 H H 0 ON- 0 184 1?I(CH2)2SCzH H 11 COCH; C0CH CONH 0 243 12 H COCH CONH 0 236 Urazole guanazole and derivatives can be easily prepared according to methods known to those skilled in the art.

In order to illustrate the preparation of compounds listed in the above table the following references are given: Compound 2: J. Prakt. Chemie 88 (1913) p. 310 Compound 4: Arch. der Pharm. 294 196i p. 270-2 Compound 5: Arch. der Pharm. 294 1961 p. 270-2 Compound 6: J. Ann. Chem. Soc. 42, 2308 Compound 7: Her. 35, p. 558 Compound 8: Anali Chim. Farm 26 (1897) p. 481-90 Compound 9: Anali Chim. Farm. 26 (1897) p. 481-90 Compound 10: Anali Chim. Farm. 26 (1897) p. 481-90 Compound 1 1: Arch. der Pharm. 294 (1961) p. 270-2 Compound 12: Anali Chim. Farm. 26 (1897) p. 481-90 In the cases wherein a nitrogen atom making part of the ring closed by Z carries a hydrogen atom having sufficient acid properties. the treating agent" can also be applied in the salt The present invention can be carried out in the manufacture of an electrophotographic recording material, by allowing the zinc oxide to come into contact with the treating agent at any stage of the manufacture. Thus, the contact can take place before or during the preparation of a photoconductive coating composition, comprising photoconductive zinc oxide and a binder material, for forming a photoconductive layer. Al-

'ternately the contact can take place after the formation of the layer, e.g., after coating a said compound onto a support.

In order to obtain the desired effects it is not necessary for the treating agent to contact the zinc oxide particles over the whole of their surfaces. Moreover, an electrographic record- 'ing material according to the invention need not comprise only zinc oxide particles which have been treated in accordance with the invention. The photoconductive layer can incorporate a mixture of treated and untreated zinc oxide grains. Some of the zinc oxide grains can be treated as described in the United Kingdom Pat. No. 1,020,504 filed Dec. 29, 1961 and Pat. No. 1,020,505 filed Nov. 8, 1961 bothby Gevaert Photo-Producten N.V.

The following methods can successfully be applied for forming a photoconductive layer composition according to the present invention.

1. The treating agent is added to an aqueous dispersion of the photoconductive zinc oxide. The treated zinc oxide is filtered off or centrifuged, dried and then dispersed in a solution of binding agent. This method is especially suited for compounds that are soluble or dispersible in water.

2. The photoconductive zinc oxide is dispersed in an organic solvent wherein the treating agent is soluble or dispersie w e svizqn t e necessary ay"? 9f FWFFEEJLB P. i added. A binding agent can be applied simultaneously or thereafter.

3. The photoconductive zinc oxide, a binding agent and a solvent for the latter are dispersed together, e.g., by grinding in a ball-mill, according to the particular zinc oxide particle size desired. The treating agent is added before, during or after grinding.

4. To a paper support a layer is applied from a composition containing the treating agent and optionally a binding agent. Alternatively, the treating agent is incorporated into the paper, e.g., during the manufacture of the paper. On top of this layer (or to the paper as the case may be) a layer is applied containing untreated zinc oxide and a binding agent. During coating of the latter layer and/or during storage of the material some treating agent diffuses from the first layer or the paper backing, to the photoconductive zinc oxide and is absorbed thereon. When this method is used and when a treating agent is employed having a marked antistatic character, the agent can be used in such an amount that a sufficient quantity thereof remains in the paper to render the latter sufficiently conductive for carrying off electrostatic charges during exposure.

5. To a paper backing is firstly applied a layer of untreated photoconductive zinc oxide, which is dispersed in a binding agent. On top of this layer a layer is applied containing the treating agent and a binding agent if desired. During coating of the second layer and/or during storage of the material, some treating agent diffuses from the second layer to the zinc oxide in the first layer. The composition of the second layer can be selected so as to impart required surface characteristics to the recording material, e.g., to render the surface suitable for application of the developing processes described and claimed in the United Kingdom Pat. No. 1,020,502 and 1,020,505 both filed Nov. 8, 1961 by Gevaert Photo-Producten N.V. It is also possible to use in the second layer a binding agent selected so that the adhesion of a developing powder thereto is either enhanced, thus enabling fixing to be improved, or decreased, thus permitting a better image transfer.

The photoconductive zinc oxide is preferably prepared by the oxidation of zinc vapor, thus is preferably so-called French-type photoconductive zinc oxide.

The dark-resistivity of a photoconductive zinc oxide layer can be increased to an optimum value by using increasing quantities of treating agents. If the amount of treating agent, which gives an optimum dark-resistivity, is exceeded, the latter decreases proportionally to the amount of excess treating agent.

It has been established experimentally that an optimum dark-resistivity is obtained by adding to the composition of the photoconductive layer during its manufacture, according to the activity of the selected treating agent (which in that case contains no cations, nor is applied in complexed form) 0.01 percent to 10 percent by weight of such agent based on the weight of the photoconductive zinc oxide. Preferably 0.01 to 3 percent of treating agent is used. The amount of treating agent required when this agent is in salt or complexed form is normally higher.

In order to obtain the same effect with corresponding salts or complexed compounds, normally amounts beyond 0.5 percent by weight in respect of the photoconductive zinc oxide are applied, e.g., between 0.5 and 40 percent.

It will be understood that if the treating agent is added to a layer or sheet adjacent to the photoconductive layer and allowed to contact the zinc oxide by diffusion, the required proportion of the treating agent in relation to the photoconductive zinc oxide generally is higher than when the treating agent is incorporated into the zinc oxide layer itself.

When a photoconductive layer is formed comprising treated zinc oxide in a binder, the ratio of binding agent to photoconductor influences the quality of the photoconductive layer with respect to the photoconductive properties, mechanical strength and insulating power. It is preferred to employ the binding agent(s) and photoconductor in weight ratio of from 1:3 to 1:9. If layers are used with a much larger proportion of binding agent, the image sharpness tends to decrease. if layers are used with much lower content of binding agent than the minimum content specified above, the mechanical strength of the coating may be insufficient for many purposes.

Photoconductive recording materials according to the present invention can be used in a wide variety of reproduction methods, and enable very contrasty images to be easily and consistently obtained, even under widely difiering circumstances such as strongly varying degrees of air humidity.

in combination with the treating agents used in the present invention binding agents possessing a higher specific dark-resistivity than the treated zinc oxide as well as binding agents possessing a lower specific dark-resistivity can be used. Suitable binding agents are described in the United Kingdom Pat. No. 964,878 filed May 3, 1960 and Pat. No. 1,020,054 filed Dec. 6, 1962 both by Gevaert Photo-Producten NV.

The said treating agents are successfully used in combination with binding agent(s) applied from an organic medium as well as in combination with binding agents applied from an aqueous medium.

Binding agents and mixtures of binding agents suitable to be applied from an aqueous medium are described in out published Dutch Pat. Application Nos. 6,608,814 and 6,608,815 both filed June 24, 1966 and 6,802,733 filed Feb. 27, 1968 Binding agents and mixtures of binding agents applied from an organic medium are, e.g., described in the United Kingdom Pat. No. 1,020,503 filed Nov. 8, 1961 and Pat. No. 1,020,504 filed Dec. 29, 1961 both by Gevaert Photo-Producten N.V.

Preferred binding agents contain acidic groups or groups from which an acid can be produced in situ. The content of acidic groups is, however, preferably not so high that the recording layer obtains a water-soluble character.

Very good results are obtained with vinyl copolymers that contain organophilic (hydrophobic) structural units and acidic structural units derived from a, ,B-ethylenically unsaturated carboxylic acid compounds, e.g., crotonic acid, acrylic acid, maleic acid, itaconic acid and methacrylic acid compounds.

Hornopolymers containing acidic structural units may be used in admixture with organophilic polymers. Polymers and copolymers from which acidic groups can be produced in situ contain, e.g., carboxylic anhydride groups, e.g., maleic anhydride groups and/or sulphonylchloride groups, which can be hydrolized to sulphonic acid groups. The photoconductive zinc oxide is preferably dispersed in an organic medium (aromatic hydrocarbon so1vent(s), chlorinated hydrocarbon solvent(s) or lower aliphatic alcohol) by means of an acidic alkyd resin, copo1y(ethylene/vinyl-sulphonyl chloride/vinyl chloride) or formaldehyde acetal of polyvinyl alcohol respectively.

Particularly suitable binding agents and binding agent mixtures for application in recording layers according to the present invention are:

a. polyvinyl acetate b. copoly(vinyl chloride/vinyl acetate/maleic anhydride) (/14/1 percent by weight) c. copoly( vinyl chloridelviriylacetatelvinyl alcohol )(9 1 /3/6 percent by weight) a. copoly(ethy1ene/vinylsulphonyl chloride/vinyl chloride) (45.2/6.2/48.6 percent by weight) I I A b. alkyd resin (acid number: 12)

3. poly(isobutyl methacrylate) 4. copoly( methyl methacrylate/isobutyl 1ate)(20/80 by weight) 5. a. poly(isobutyl methacrylate) b. formaldehyde-acetal of polyvinyl alcohol 6. copoly(vinyl acetate/crotonic acid) (94.6/5.4 percent by weight) methacrya. copoly(vinyl acetate/crotonic acid) (93.4/6.6 percent by weight) b. copoly(ethylene/vinylsulphonyl chloride/vinyl chloride) (45 .2/6.2/48.6 percent by weight) a. copoly(vinyl acetate/methyl acrylate/acrylic acid) (67/28/5 percent by weight) 1 b. copoly(ethylene/vinylsulphonyl chloride/vinyl chloride) -ii-ZilfE-fi. aqrssmllvlq h a- 9.

a. styrolated alkyd resin b. copoly(vinyl chloride/vinyl acid)(86.5/l3.3/0.2 percent by weight) 10. copoly(vinyl acetate/methyl acrylate/acrylic acid) (87/12/1 percent by weight) 1 l. copoly(styrene/methyl acid)(55/44.6/0.4 percent by weight) The treating agents applied in the present invention do not exclude the increase of photosensitivity of the recording element, e.g., by spectral sensitization of the photoconductive zinc oxide.

The spectrally sensitizing dyes can be allowed to adsorb to the photoconductive zinc oxide before, during and/or after the dark-resistivity increasing treatment. Spectral sensitizing agents which can be applied are described in the already mentioned United Kingdom Pat. No. 1,020,504 and in our published Dutch Pat. application Nos. 6,717,400 filed Dec. 20, 1967, 6,805,983 filed Apr. 26, 1968 No. 6,704,706 filed Apr. 3, 1967 and No. 6,704,768 filed Apr. 4, 1967. A very suitable technique for applying the spectral sensitizing agents is described in the published Dutch Patent application No. 6,704,768 which technique can also be applied successfully in respect of the dark-resistivity increasing compounds used according to the present invention.

The photoconductive recording layers containing a treating agent for photoconductive zinc oxide as described may contain in addition to the photoconductive substance and binder any other type of dark-resistivity or sensitivity increasing compound, e.g., the phosphorous compounds and other dark'resistivity increasing compounds described in the Belgian Pat. No. 612,102 filed Dec. 29, 1961 by Gevaert Photo-Producten N.V., and additives known in the coating techniques, e.g., dispersing agents (see, e.g., our published Dutch Pat. application No. 6,712,156 filed Sept. 5, 1967), compounds influencing the gloss and/or the wear resistance of the coating, and, compounds that counteract aging and/or oxidizing of the;

acetate/acrylic acrylate/acrylic layer, or that influence the thermal stability. When selecting. any additives, preference is given to those which least reduce the sensitivity and dark-resistivity of the photoconductive layer.

The photoconductive composition treated according to the present invention may be coated on a support according to a known coating technique, e.g., by spraying, whirling, dip-coating, or by a coating technique wherein use is made of a doctor blade. The supports or base materials are chosen in view of the particular charging, exposure, recording and/or transfer technique wherein the recording material is used.

In the electrophotographic recording techniques, wherein the photoconductive layer is electrostatically charged, the

support has an electric volume resistivity lower than that of the recording layer, preferably at least 10 as low as that of the photoconductive recording layer. Suitable supports are described, e.g., in the United Kingdom Pat. No. 995,491 filed Mar. 16, 1962, No. 1,020,503 filed Nov. 8, 1961 and No. 1,020,504 filed Dec. 29, 1961 all by Gevaert Photo-Producten N.V. and in the U.S. Pat. No. 3,008,825 of Warren G. Van Born and Osmar A. Ulbrich Jr., issued Nov. 14, 1961. Preferably used supports are conductive paper supports, more preferably glassine type paper supports.

The photoconductive layer of an electrophotographic material which is prepared by starting from a coating composition according to the present invention, can be used for recording purposes, in which prior to exposure an electric charge is nondifferentially applied according to known methods. However, the material can also be used in recording techniques, in which the exposure step precedes the charging step. For such a technique we may refer to, e.g., the United Kingdom Pat. Nos. 1,033,419 and 1,033,420 both filed Nov. 26, 1962 by Gevaert Photo-Producten N.V.

The charging as already explained can be effected with a negative as well as with a positive corona.

A corona charging system suited for a rapid change from negative to positive corona charging operates with a so-called floating earth having corona wires of opposite charge sign under and in front of the recording layer to be charged.

Well-established methods of developing electrostatic images include cascade-, powder cloud-, magnetic brushand fur brush-development. These methods are based on the application of charged dry toner to the surface bearing the electrostatic image. Other methods are based on the use of liquids, either insulating (electrophoretic development which is preferred) or conductive liquids (see, e.g., the U.S. Pat. No. 2,907,674 of Kenneth A. Metcalfe and Robert J. Wright, issued Oct. 6, 1959 and the Belgian Pat. No. 610,060 filed Nov. 8, 1961 and No. 625,335 filed Nov. 27; 1962 both by Gevaert Photo-Producten N .V.). Development of a conductivity image based on electrolysis is described, e.g., by J. A. Amick, RCA Rev., 20, 753 (1959).

The present invention is further illustrated by the following examples.

EXAMPLE 1 2,309 g. of a 20 percent solution in dichloroethane of HYPALON 30 (registered trademark for a copoly(ethylene/vinylsulphonyl chloride/vinyl chloride) (26.1/6.9/67 percent by weight) marketed by E. I. du Pont de Nemours & Co. (Inc.) Wilmington, Del.,) where diluted ,with 535 ml. of dichloroethane, 560 ml. of methyl ethyl ketone and 112 ml. of ethanol. While stirring 1,820 g. of photoconductive zinc oxide (marketed by Vieille Montagne S.A. ds iita ueaens s s"? uma a Eight hundred and eighty grams of the obtained dispersion were further diluted with 508 g. of dichloroethane, 17 g. of ethanol and g. of methyl ethyl ketone, and the sensitizing xsmvinat iql qu saf was 0H Br 0 Br S 03 respectively L23 ml. of a 1 percent solution in methanol and 4.4 ml. of a 0.5 percent solution in dimethylformamide, where admixed.

In order to lower the memory effect of a recording layer containing the said composition, 9 ml. of a 10 percent solution of el n m th l e tnami rtee eed- ,7

The coating composition containing urazole and a same coating composition without urazole were applied in the same conditions to a glassine paper support and conditioned after drying at 20 C. and 50 percent of relative humidity.

The following results were obtained on measurement by means of the rotating disc device as already described.

Negative coronafeharging imgiediately tolloyzlnga sec;

nds 500 lux pre-exposm-e Negative coronacharging without previous exposure of the recording layer Maximal Charging time Maximal Chargi g time 2 5 charging for reaching charging for r achlng level 90% of the level 90% or the expressed maximal level expressed maximal level in volts (10- sec.) lrr volts (10" sec.)

300 40 225 70 Urazole-. 325 16 325 15 EXAMPLE 2 in methanol were used. As memory-effect results comparable to those of the table in example 1 the following data were obtained (without prior exposure): 310 v./l7.l0' sec., after prior exposure: 300 v./l 7. l0 sec.

EXAMPLE 3 One hundred and one grams of HYPALON 30 (registered trademark) were dissolved in a mixture of 575 ml. of dichloroethane, 156 ml. of methyl ethyl ketone, and 31 ml. of ethanol. As dispersing agent for the photoconductive pigments 19.5 ml. of a 80 percent solution in toluene of CEL- LOLYN 95 (an acid alkyd resin marketed by The Hercules Powder Company Inc., Wilmington, Del., were added to this solution. Thereupon 447 g. of photoconductive zinc oxide (Type A Neige extra pur-Vieille Montague S.A., Belgium) and 61 g. of CADMOPUR GOLDGELB N (trade name of Farbenfabriken Bayer AG LeverkusenW. Germany, for a cadmium sulphide pigment containing 76 percent of cadmium. 22 percent of sulphur, 2 percent of a mixture of barium sulphate and silica, and traces of zinc and selenium were admixed while stirring. To the pigment dispersion 4 ml. ofa 10 percent solution of urazole in dimethylformamide were added and intimately mixed therewith. The pigment composition was then put once through a sand-mill (Sandmill-Sussmeyer, Type IA) at a rate of24 liters/h).

The dispersion was coated onto glassine paper at a rate of 33 g. of solids per sq.m. The coating was dried in a laminar current drier at 30-40 C. (air rate 7 m./min). A smooth surface was obtained.

The dried material was charged with a double corona, the corona wires in front of the recording layer and those below the support having a potential difference of 5000 v. and +5000 v. respectively in respect of the ground.

A step wedge with constant of 0.1 was projected on the recording layer by means of a set of incandescent lamps. The exposed material was electrophoretically developed with a hydrocarbon solvent-carbon dispersion.

The developed image proved that the recording layer was suited for the production of images with a steep gradation so that text originals were reproduced with a very sharp letter on a clear background. The images showed a high density and the recording material proved to have a small memory effect and a high sensitivity to light.

EXAMPLE 4 Six hundred and eighty-four milliliters of a 57.5 percent by weight solution in toluene of copoly(vinyl acetate/methyl acrylate/acrylic acid) (87/ 12/ 1 percent by weight) were diluted with 3,316 mi. of toluene. While stirring the following ingredients were added:

French type hotoconductive zinc oxide (average particle size 0.5 p.) 2.400 kg. [0% by weight solution of urazole in dimethylformamide l9.2 ml. 1% by weight solution of bromophenol blue in methanol l8 ml.

0.5% by weight solution of -CH=CHCH=(IJ Br- I N (CH2)4S O2NHCOCH: L ONHFJJOCH This dispersion was treated in a sand-mill till an average grain size of 0.15 ,a was obtained, whereupon the homogenized dispersion was coated onto a glassine paper of g./sq.m at a rate of 30 g. of solids per sq.m. The coated layer was dried in a laminar current drier.

The dried material was negatively corona-charged till 500 v. with a double corona, the corona wires in front of the recording layer and below the support having a potential difference of 5000 v. and +5000 v. respectively in respect of the so-called floating earth.

The charged recording layer was projection-exposed for 3 see. by means of an incandescent tungsten filament lamp of watt/12v. placed at a distance of 30 cm., through a linework transparency (diapositive) and developed in an electrophoretic developer on the basis of positive toner particles.

A positive 7 X enlarged reproduction of the diapositive was obtained. The developer was produced by diluting the concentrated developer composition described hereinafter in a volume ratio of 15/1000 by means of lSOPAR H (trade name for an isoparaffinic hydrocarbon mixture having a boiling range of l77-l88 C., sold by Esso Belgium N.V., Antwerp, Belgium):

ll 12 carbon black (average particle size: 20 nm.) 30 g. zinc monotridccyl phosphate as dispersing agent 1.5 g. ISOPAR H (trade name) 750 ml. resin solution prepared as 5 described hereinafter 150 g.

The resin binder solution was prepared by heating 500 g. of ;E Q.-

ALKYDAL L 67 (trade name of Farbenfabriken Bayer A.G.,' l Leverkusen, W. German, for a linseed oil-modified (67 percent by weight) alkyd resin and 500 ml. of white spirit contain- EXAMPLE 7 ing 1 1 percent by weight of aromatic compounds at 60 C. tillf EFEFfiEQFBIlQFYi l l qll'iqi l q lfilipiii fll E'L BE;

The same favorable results were obtained.

Example 5 was repeated, except that the urazole was replaced by a same amount of the compound having the fol- The same recording layer was positively corona-charged till 1 lowing formula:

+500 v. with the same double corona unit of which the corona wires in front of the recording layer and those below the sup- H port had a potential difference of +5,000 v. and 5,000 v. respectively in respectto the floating earth. g O=C NH The positively charged recording layer was exposed in the QTQH EN .f same optical enlarger as described above but with a negative i fil image as the original The same favorable results were obtained.

By using the same developer as described above, a 7 X en- EXAMPLE 8 larged reproduction having reversed image values in respect of the negative microfilm image was obtained. Three hundred and sixty grams of copoly( vinyl acetate/crotonic acid) (95.7/4.3 percent by weight) were dissolved in a mixture of 21.4 I. of dichloroethane and 1.6 l. of K E 5 V A 7 ethanol. To the solution of the binder 12 kg. of photoconductive zinc oxide (French type) of an average particle size of 0. l5 p., and 8 l. of methyl isobutyl ketone were added. The obtained mixture was homogenized in a sand-mill and to 43.280 kg. of the obtained dispersion were added while stirring:

88.8 ml. of a 10 percent by weight solution of urazole in dimethylformamide 1,665 g. of HYPALON 30 (trade name for a copoly(ethylene/vinylsulphonyl chloride/vinyl chloride) To the dissolved binding agent mixture 1.200 kg. of (26.l/6.9/67 percent by weight) marketed by E. l. du Pont de Three hundred and five ml. milliliters a 55 percent by weight solution in ethanol of copoly(vinyl acetate/methyl acrylate/acrylic acid) (molar ratio 672285) were diluted with 3,040 ml. of sym.-dichloroethane and 810 ml. of cyclohexanone. In the obtained solution 120 g. of polyvinyl acetate 1 ende Lil photoconductive zinc oxide v g p icl iz I Nemours & Co. (Inc), Wilmington, Del.,) dissolved in 8.325 prepared by the oxidation of zinc vapor were added and inti- 40 l. of sym.-dichlorethane, niately mixeg with: V V d g 7 h 162 ml. of a 0.5 percent solution of lndlmethylformamide a 10% by weight solution of 45.5 ml. of a 1 percent by weight solution of bromophenol urazole ln dimethylformamide 9.6 ml. blue i h l a 1% by weight solution of The obtained dispersion was applied by knife coating to a conductive paper base of 67 g./sq.m at a rate of 25 g. of solids 1 per sq.m. The obtained layer was dried at 80f bromophenol blue in methanol l2 ml. 3 0.5% by weight solution or The obtained mixture was homogenized, filtered and oin d The dried recording layer was negatively corona-charged at a rate of 27 g. of solids per sq.m onto a glassine paper contill -600 v. with a double corona, the corona wires in front of taining conductivity-increasing salts. the recording layer and those below the support havlrllg a The coated layer was dried in a laminar current drier at 60 P n i l difference -i and +1 respecllve y respect of the ground. 7

The P and Pmcessing proceeded as descl'ibm The charged recording layer was projection-exposed for 10 ample 4. and the same favorable results were obtained. b eans of an incandescent tungsten fil ment mp f 400 watt placed at a distance of 40 cm. through a positive EXAMPLE 6 linework transparency and developed by means of an elec- Example 4 was repeated, except that the urazole was PPPP Y QPV"? "3 ll replaced by a same amount of the compound with the follow- A positive 7 X enlarged reproduction of the positive transing for I parency was obtained.

v. respectively in respect of the floating earth.

The positively charged recording layer was exposed in the same optical enlarger as described above but to a negative microfilm image as an original.

By using the same developer as described in example 4, a 7

X enlarged reproduction having reversed image values in 10 respect of the negative microfilm image was obtained.

EXAMPLES 9-10 Example 8 was repeated, except that the urazole, was

replaced by a same amount of one of the compounds of the f rn l sm. H

0=I NH Q and H HN=C NH respectively.

, EXAMPLE 11 Five hundred and twenty-five grams of copoly(vinyl chloride/vinyl acetate/maleic anhydride) (85/ 14/ 1 percent by weight) were dissolved in 39.5 i. of sym.-dichloroethane. To this solution the following composition was added:

Two hundred and eighty milliliters of a 10 percent by weight solution of monobutyl phosphate in ethanol 2.720 1. ofethanol 90 ml. of a 10 percent by weight solution of urazole in dimethylformamide 447 g. df copoly(vinyl chloride/vinyl acetate/vinyl alcohol)(9 1/3/6 percent by weight dissolved in a mixture of2 l. of sym.-dichloroethane and 224 ml. of ethanol 1,548 g. of coply( vinyl acetate/vinyl lurate (80/20 percent by weight) 47 ml. of a 1 blue in methanol 50 ml. ofa 0.5 percent by weight solution of percent by weight solution of bromophenol sulating recording element comprising photoconductive zinc oxide treated with a compound corresponding to the following general formula and the salt form and tautomeric structures thereof:

wherein each of R,, R and R represents hydrogen, an alkyl group, acyl group, an aryl group, or a at least one of R R or R being hydrogen.

2. A method for recording and reproducing information according to claim 1, wherein the photoconductive zinc oxide has been dispersed in a binder medium containing at least one binding agent comprising acidic groups or groups from which an acid can be produced in situ.

3. A method for recording and reproducing information according to claim 2, wherein said binding agent is a vinyl copolymer containing hydrophobic structural units and acidic structural units derived from afl-ethylenically unsaturated carboxylic acid compounds.

4. A method for recording and reproducing information according to claim 2, wherein the groups from which an acid can be produced in situ are carboxylic anhydride groups or sulphonyl chloride groups.

5. A method for recording and reproducing information according to claim 1, wherein the photoconductive zinc oxide is used in admixture with a substance increasing its spectral sensitivity.

6. A method for recording and reproducing information comprising the step of forming an information wise electrostatic charge pattern by electrostatically charging and information-wise exposing to active electromagnetic radiation an electrophotographic recording material containing a photoconductive recording layer comprising photoconductive zinc oxide treated with a compound corresponding to the following general formula (including its salt and tautomeric structures):

wherein each of R,, R and R represents hydrogen, an alkyl group, acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R,, R R being hydrogen.

7. A method for recording and reproducing information according to claim 6, wherein the electrostatic charge pattern formed on said layer is made visible by development with electrostatically attractable material.

A metho d for recording and reproducing information as:

(CHzM-SOzNH-COCHa (Hrh-S OmH-G O CH;

i dimethyltormamlde The obtained dispersion was coated at a rate of 27 g. solids per sq.m onto a glassine paper of g./sq.m, and the coated. 7O

1. A recording process wherein an information-wise pattern:

of increased conductivityprgducedin a photoconductive incording to claim 6, wherein the recording layer has been applied to a conductive layer or support having a volume resistivity lower than that of the dark-adapted recording layer.

9. A method for recording and reproducing information according to claim 8, wherein the support is a paper support.

10. A method for recording and reproducing information according to claim 6, wherein said compound is used in admixture with the pho toconduc tive zinc oxide in an amount of tive zinc oxide.

11. A method for recording and reproducing information according to claim 6, wherein the photoconductive zinc oxide has been used in admixture with an organic oxyacid of phosphorus increasing the dark-resistivity of the photoconductive zinc oxide.

12. A method for recording and reproducing information according to clan- 6, wherein the recording layer is electrostatically negatively charged. a

13. A method for recording and reproducing information according to claim 6, wherein the recording layer is electrostatically positively charged.

14. A method for recording and reproducing information according to claim 12, wherein after charging and information-wise exposure the formed electrostatic charge pattern is developed electrophoretically.

15. A method for recording and reproducing information according to claim 13, wherein after charging and information wise exposure the formed electrostatic charge pattern is developed electrophoretically.

16. A recording material containing photoconductive zinc oxide treated with a compound corresponding to the following general formula (including its salt and tautomeric structures):

wherein each of R R and R represents hydrogen an alkyl group, acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R,, R or R being hydrogen.

17. A recording material accordingto claim 16, wherein the said compound is added to the composition of the layer containing the zinc oxide in an amount of 0.01 to 10 percent by weight in respect of the photoconductive zinc oxide.

18. A recording material according to claim 16, wherein the photoconductive zinc oxide has been dispersed in a binder medium in a ratio by weight of from 1:3 to 1:9.

l0 groups from which an acid can be produced in situ are carbox- 19. A recording material according to claim 4, wherein in the photoconductive zinc oxide as been dispersed in a binder medium containing at last one binding agent comprising acidic groups or groups from which an acid can be produced in situ.

20. A recording material according to claim 19, wherein said binding agent is a vinyl copolymer containing hydrophobic structural units and acidic structural units derived from a, B-ethylenically unsaturated carboxylic acid compounds.

21. A recording material according to claim 19, wherein the ylic anhydride groups or sulphonyl chloride groups.

22. A recording material according to claim 16, wherein the photoconductive zinc oxide has been used in admixture with an organic oxyacid of phosphorus.

23. A recording material according to claim 16, wherein the photoconductive zinc oxide has been spectrally sensitized.

24. In an electrophotographic process for the production of positive or negative reproduction selectively of an original by means of (1) a same photoconductive recording material and developing material having a particular electrical charge polarity and (2) by the choice of the polarity of the electrostatic charge applied to the photoconductive recording element of the photoconductive recording material, the use of a photoconductive recording element comprising photoconductive zinc oxide that has been treated with a compound corresponding to the following general formula (including its salt and tautomeric structures):

l a O=C N-Rz wherein each of R,, R and R represents hydrogen, an alkyl group acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R R or R, being hydrogen.

25. In an electrophotographic process according to claim 24 wherein the recording material after charging is exposed to an original in the form of at last one microfilm image.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,634,080 Dated January 11, 1972 Patent No.

Robert Joseph NOE et al Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 14, claim 1, line 14, before "at least", insert pyridine nucleus, or a thiazole nucleus;

Column 16, claim 19, line 1, change "4" to l6 Signed and sealed this 30th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCI-IER,JR. ROBERT GOTTSCI-IALK Commissioner of Patents Attesting Officer USCOMM-DC 50376-P69 U. 5. GOVIRNMINT PRINTING OFFICE I... O-fiGl-SM FORM PC4050 (10-69) 

2. A method for recording and reproducing information according to claim 1, wherein the photoconductive zinc oxide has been dispersed in a binder medium containing at least one binding agent comprising acidic groups or groups from which an acid can be produced in situ.
 3. A method for recording and reproducing information according to claim 2, wherein said binding agent is a vinyl copolymer containing hydrophobic structural units and acidic structural units derived from Alpha Beta -ethylenically unsaturated carboxylic acid compounds.
 4. A method for recording and reproducing information according to claim 2, wherein the groups from which an acid can be produced in situ are carboxylic anhydride groups or sulphonyl chloride groups.
 5. A method for recording and reproducing information according to claim 1, wherein the photoconductive zinc oxide is used in admixture with a substance increasing its spectral sensitivity.
 6. A method for recording and reproducing information comprising the step of forming an information wise electrostatic charge pattern by electrostatically charging and information-wise exposing to active electromagnetic radiation an electrophotographic recording material containing a photoconductive recording layer comprising photoconductive zinc oxide treated with a compound corresponding to the following general formula (including its salt and tautomeric structures): wherein each of R1, R2, and R3 represents hydrogen, an alkyl group, acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R1, R2, R3 being hydrogen.
 7. A method for recording and reproducing information according to claim 6, wherein the electrostatic charge pattern formed on said layer is made visible by development with electrostatically attractable material.
 8. A method for recording and reproducing information according to claim 6, wherein the recording layer has been applied to a conductive layer or support having a volume resistivity lower than that of the dark-adapted recording layer.
 9. A method for recording and reproducing information according to claim 8, wherein the support is a paper support.
 10. A method for recording and reproducing information according to claim 6, wherein said compound is used in admixture with the photoconductive zinc oxide in an amount of 0.01 to 10 percent by weight in respect of the photoconductive zinc oxide.
 11. A method for recording and reproducing information according to claim 6, wherein the photoconductive zinc oxide has been used in admixture with an organic oxyacid of phosphorus increasing the dark-resistivity of the photoconductive zinc oxide.
 12. A method for recording and reproducing information according to claim 6, wherein the recording layer is electrostatically negatively charged.
 13. A method for recording and reproducing information according to claim 6, wherein the recording layer is electrostatically positively charged.
 14. A method for recording and reproducing information according to claim 12, wherein after charging and information-wise exposure the formed electrostatic charge pattern is developed electrophoretically.
 15. A method for recording and reproducing information according to claim 13, wherein after charging and Information wise exposure the formed electrostatic charge pattern is developed electrophoretically.
 16. A recording material containing photoconductive zinc oxide treated with a compound corresponding to the following general formula (including its salt and tautomeric structures): wherein each of R1, R2, and R3 represents hydrogen an alkyl group, acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R1, R2, or R3 being hydrogen.
 17. A recording material according to claim 16, wherein the said compound is added to the composition of the layer containing the zinc oxide in an amount of 0.01 to 10 percent by weight in respect of the photoconductive zinc oxide.
 18. A recording material according to claim 16, wherein the photoconductive zinc oxide has been dispersed in a binder medium in a ratio by weight of from 1:3 to 1:9.
 19. A recording material according to claim 4, wherein in the photoconductive zinc oxide as been dispersed in a binder medium containing at last one binding agent comprising acidic groups or groups from which an acid can be produced in situ.
 20. A recording material according to claim 19, wherein said binding agent is a vinyl copolymer containing hydrophobic structural units and acidic structural units derived from Alpha , Beta -ethylenically unsaturated carboxylic acid compounds.
 21. A recording material according to claim 19, wherein the groups from which an acid can be produced in situ are carboxylic anhydride groups or sulphonyl chloride groups.
 22. A recording material according to claim 16, wherein the photoconductive zinc oxide has been used in admixture with an organic oxyacid of phosphorus.
 23. A recording material according to claim 16, wherein the photoconductive zinc oxide has been spectrally sensitized.
 24. In an electrophotographic process for the production of positive or negative reproduction selectively of an original by means of (1) a same photoconductive recording material and developing material having a particular electrical charge polarity and (2) by the choice of the polarity of the electrostatic charge applied to the photoconductive recording element of the photoconductive recording material, the use of a photoconductive recording element comprising photoconductive zinc oxide that has been treated with a compound corresponding to the following general formula (including its salt and tautomeric structures): wherein each of R1, R2, and R3 represents hydrogen, an alkyl group acyl group, an aryl group, or a pyridine nucleus, or a thiazole nucleus at least one of R1, R2, or R3 being hydrogen.
 25. In an electrophotographic process according to claim 24 wherein the recording material after charging is exposed to an original in the form of at last one microfilm image. 